Measurement of stamped parts (from coiled metal)

[ryandias]

I work for an electronics company, we use a lot of stamped copper parts. We have a power module that will get molded as a single stamped array of lead frames. This will be cropped to make the individual circuits later.

Some of the GD&T is being debated with us from the supplier. The issue is datum A. Datum as is the plane in which the metal lies, but in the real world it has memory of being coiled up. So this datum should be stated, while being constrained I suppose, but I have never seen this in practice/drawing.

Can you guys supply examples of how datums are stated, and understood to be constrained? held down?

 

[KENAT]

ASME Y14.5M-1194 has a little in it at section 6.8 Free State Variation

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ryandias]

Thanks KENAT!

 

[Belanger]

Yep -- simply add a note stating that "geometric tolerances are to be checked while part restrained under such-and-such force at such-and-such points," etc.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[drawoh]

ryandias,

Many of my drawings of sheet metal and of plates state "DATUM[ ]A APPLIES WHEN THE FACE IS CLAMPED TO A FLAT REFERENCE SURFACE.". The ASME[ ]Y14.5 chapter on free state gives you a lot of possibilities.

--
JHG

 

[dgallup]

I also have some sheet metal parts that have to be measured when snapped onto a gauge pin or sometimes a fixture.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[tbuelna]

ASME Y14.5-2009 sections 4.20 and 5.5 provide guidance on datums/tolerancing with a part in a restrained condition. As others noted, you need to provide detailed instructions on how to restrain the part as well as any specific inspection equipment/fixtures required. With the example given in the OP, it would not be sufficient to simply state the datum is established with the part in a restrained condition. The configuration of the inspection restraining fixture and the restraining force applied to the part must be sufficient to produce a consistent result given the range of free state shapes existing in the stamped parts.